1. Field of the Invention
This invention relates to transfer processes in the treatment of molten iron and iron alloys by electro-thermic processes. The invention particularly relates to a technique for preparing ingots of various steel composition directly from prereduced iron ore pellets utilitzing a two-furnace process on a continuous basis. The invention incorporates a primary, single-phase AC electric arc furnace and a conventional cold-mold electroslag furnace. The process is particularly suitable for use at versatile small steel plants which are interested in inexpensive methods to serve customers with small tonnages of high quality steel ingots of particularly unique alloy composition.
2. Background of the Invention
Several years ago, increasing scrap shortages, decreasing quality and high scap costs made it necessary for the steelmakers to consider prereduced iron ore pellets as a supplemental charge material for electric arc furnaces. In a relatively short time, advantages of using prereduced iron ore pellets became apparent, and considerable success has been experienced in the development of efficient processes for their utilization in the preparation of a variety of steels. The use of prereduced iron ore pellets still requires, in conventional electric-arc furnace steelmaking, various degassing, casting, and conditioning steps to produce the desired quality material.
In an effort to simplify the operations, reduce costs, and minimize capital investments, the technique of electroslag melting was adopted which is particularly suitable for small tonnages. One disadvantage of using conventional electroslag techniques to melt prereduced iron ore pellets is that gangue oxides such as FeO, SiO.sub.2, MgO, CaO, and Al.sub.2 O.sub.3 are not easily handled without electrode and ore flux additions or with an additional prereduction step. This generally requires the formation of a consumable electrode of the proper composition and also generally requires a 92-93% metalization. Since the conventional electroslag process is a secondary melting technique, ingots with optimum properties are more easily and less expensively obtained if the gangue impurities have been removed prior to electroslag melting.